Question

Study of the presence of oxalate ions in guava fruit at different stages of ripening.

Answer 1

Hint: Guava fruit is rich in vitamin C, consisting of oxalate ions in large amounts. It is a carboxylic acid. The presence of oxalate ions in guava fruit can be studied with the help of potassium permanganate.

Complete step by step answer:
First, let us know about the oxalate ions, it is produced in our body itself, or attained from vitamin C by converting it into oxalate ions.
Now, we will study the presence of oxalate ions by performing an experiment step by step.

The first step is weighing about 50 g of fresh guava, and crushing it to a fine pulp.
Second, we have to transfer the crushed pulp to a beaker, and add 50 ml of dilute sulphuric acid to it.
Then, boil the content for about 20 minutes, and in 100 mL flask cool, and filter the contents.
Now, add distilled water in a flask to make it up to 100 mL.
Further proceeding with the experiment, take out 20 mL of the solution from the flask, and add 20 mL of dilute sulphuric acid to it.

Now, we have to heat the mixture to about 60$\circ$ C, and in a burette we will titrate it against N/10 potassium permanganate solution till the end point appears i.e. pink colour.
Repeat the experiment with 50 g of 1 day, 2 days and 3 days old guava fruit.
At last, we will observe the end point for raw guava, semi-ripened, and ripened guava, and the content of oxalic acid grows with ripening of guava.

Note: Be careful while performing the experiment. The chemicals should be added properly. The most important is the burette should be without a rubber tap, as potassium permanganate solution attacks rubber. If the addition of potassium permanganate brown colour appears then it indicates towards the insufficient addition of sulphuric acid. In that case, prepare the solution again for titration.